Remote Ua Behind Nat; Sip Signaling Messages - AudioCodes Mediant 4000 SBC User Manual

Parameter
Target End Port
target-end-port
[NATTranslation_TargetEndPort]

11.7.2 Remote UA behind NAT

This section describes configuration for scenarios where the device sends signaling and
media packets to a remote UA that is located behind NAT.

11.7.2.1 SIP Signaling Messages

By default, the device resolves NAT issues for SIP signaling, using its NAT Detection
mechanism. The NAT Detection mechanism checks whether the endpoint is located behind
NAT by comparing the incoming packet's source IP address with the SIP Contact header's
IP address. If the packet's source IP address is a public address and the Contact header's
IP address is a local address, the device considers the endpoint as located behind NAT. In
this case, the device sends the SIP messages to the endpoint using the packet's source IP
address. Otherwise (or if you have disabled the NAT Detection mechanism), the device
sends the SIP messages according to the SIP standard (RFC 3261), where requests within
the SIP dialog are sent using the IP address in the Contact header, and responses to
INVITEs are sent using the IP address in the Via header.
If necessary, you can also configure the device to always consider incoming SIP INVITE
messages as sent from endpoints that are located behind NAT. When this is enabled, the
device sends responses to the INVITE (to the endpoint), using the the source IP address of
the packet (INVITE) initially received from the endpoint. This is useful in scenarios where
the endpoint is located behind a NAT firewall and the device (for whatever reason) is
unable to identify NAT using its regular NAT Detection mechanism. This feature is enabled
per specific calls using IP Groups. To configure this feature, use the 'Always Use Source
Address' parameter in the IP Groups table (see ''Configuring IP Groups'' on page 351). If
this feature is disabled, the device's NAT detection is according to the settings of the global
parameter, 'SIP NAT Detection' parameter (see below procedure).

To enable the NAT Detection feature (global):
1. Open the Transport Settingspage (Setup menu > Signaling & Media tab > SIP
Definitions folder > Transport Settings).
2. Under the General group, from the 'SIP NAT Detection' drop-down list
(SIPNatDetection), select Enable.
3. Click Apply.
User's Manual
in the 'o=' and 'c=' SDP fields.
Defines the optional ending port range (0-65535) of the
global address. If not configured, the ports are not replaced.
Matching source ports are replaced with the target ports.
This address is set in the SIP Via and Contact headers and
in the 'o=' and 'c=' SDP fields.
Figure 11-7: Enabling SIP NAT Detection
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Mediant 4000 SBC
Description
Document #: LTRT-42025